The general manager of the Boston-area public transit system resigned Wednesday amid commuter frustration over service disruptions during a spate of recent snowstorms that have pounded the region.

Beverly Scott gave no specific reason for her surprise resignation, effective April 11, in a letter to John Jenkins, chairman of the Massachusetts Bay Transportation Authority’s board of directors.

Scott said she would give priority during her last two months on the job to restoring "normalcy" on the T after the recent disruptions, which included a complete shutdown of rail service Monday night and all day Tuesday.

The resignation came a day after Scott delivered a spirited defense of her decision to shut the system down, forcing hundreds of thousands of riders to make alternate travel plans.

At a news conference Tuesday, Scott cited breakdowns in aging equipment used by the nation’s oldest public transit system, pointing to dozens of trains that became disabled during the most recent storm that dropped more than 2 feet of snow on parts of the Boston area.

"No question, much more remains to be done to achieve the modern, and first-class public transportation system that all want and deserve," Scott said in her letter.

The MBTA board will choose a successor for Scott. Jenkins said he is "stunned" by her departure.

"Be clear, this board has had no discussions at any time about her tenure as general manager," Jenkins said in a statement. "We hoped and expected that she would fulfill her three year contract, which ends in December of this year."

The board gave Scott a vote of confidence just hours before she submitted her letter of resignation.